Hon, we didn't used to have a regen buff in solo content. This made certain solo content, even job specific quests, extremely challenging on certain jobs. It's really not that different from the fact that while Titan-Egi was pretty much always shit, the removal of Titan-Egi as an actual tank pet had people legitimately worried about how one would do quite a few of the solo duties in both the summoner job quests and MSQ as Summoner.
You're also ignoring the fact that more than half the general population of the game *are* in fact bad players (which is fine, they have a right to enjoy the game, too), and if there's any content that it's reasonable to give them an extra boost on, it's *solo* content that's intended for *everyone* to enjoy.